Floating subs are known to those skilled in the art as evidenced by the prior art of record in this patent application. Floating subs are normally placed on a drilling rig between the top drive head and the drill string. The sub's floating or axial slipping motion allows the driller to more confidently manage his drill string by removing feed cylinder and pipe weight forces from thread flanks during make-up or breakout of tool joints. Secondly, a floating sub incorporating an adequately designed shock absorbing element within itself, allows the sub to have the further advantage of eliminating a high percentage of the destructive vibrational forces transmitted to the hydraulic motor and gear box of the drilling rig. These forces are ever present by the very nature of the act of drilling a borehole through various formations no matter what type rotary bit or system is used.
Downhole shock absorbers are known to those skilled in the art. A downhole shock absorber can also reduce some of the harmonic motion transmitted between the drill bit and the drill string. A properly designed shock sub placed directly above a drill bit, directly above a downhole hammer tool, or adjacent to any stabilizers that may be included in the string, is very desirable because it can greatly extend the life of the drill bit as well as the life of the entire tool string. Furthermore, it is not uncommon for this type drill string assembly to also increase penetration rates.
According to the present invention, the use of a floating sub incorporating a shock absorbing element in combination with a top drive system, and a downhole shock sub in combination with a drill bit can be simultaneously employed and thereby obtain results not expected of prior art floating subs and shock absorbers. Accordingly, the present invention provides improvements in a floating sub for a drilling rig. The present invention further comprehends improvements in a shock absorber for use downhole in a drill string. Further, the present invention comprehends the employment of both a floating sub located at the upper end of the drill string and a shock absorber located at the lower end of the drill string. The combination of both a shock absorber and a floating sub, made in accordance with the present invention, has a synergistic effect with respect to wear on a top drive system and rate of penetration of the drill bit.